Playing in "Straight fourths"
Playing with the guitar tuned in perfect fourths has some advantages, and some drawbacks, and here's my take on the issue. One of the major problems is the almost complete lack of instructional material, so here's my little guide on how to play the basic chords and scales.
The characteristic of the straight fourths (also called "all fourths", "perfect fourths", P4s) tuning is that the interval between any string and the next one is always a perfect fourth (5 semitones). The most typical tunings are the ones closer to the standard tuning, so, from the lowest note: E A D G C F, or Eb Ab Db Gb B E. The first one has the advantage of having only two strings differently tuned. The second one (the one I use) has the advantages of not increasing the tension on the two strings that break the most often, and of making "jazz tonalities" (Eb, Bb) more accessible to open strings.
Because of the uniform interval between the strings, intervals survive vertical (across the frets) AND horizontal (ancross the strings) translations, that is, we can move the any interval we play to any other fretboard position and it will not change. For this reasons the chord and scale diagrams that I will present will not contain the indication of where (strings and frets) they are played. Move them around and they will still work.
The diagrams will look like the following
In tablature form the above chord could be for example played as
In the diagrams the vertical lines represent the frets while the horizontal spaces represent the strings (many books have the chords diagrams written vertically instead. I find this horizontal mode a bit more intuitive, since the guitar neck is usually more horinzontal then vertical, and that's how I visualize it my head. It is also consistent with the tablature notation). The above diagram covers three frets and four strings. The symbols contained in the diagram indicate the interval value of the notes played. R is Root, 5 is firth, 7- minor seventh, 3- minor third. The only strange thing is the dot "•". It's just a visual clue that shows where the roots are. They are usually not played (in fact on that string the minor seventh is played two frets below), but it's handy to have them around to visually identify intervals distant from the played root.
Because of the regular nature of the tuning the notes repeat at regular intervals over the whole fretboard
you will always find the same note (name) either "two stings up and two frets up", or "thee strings up and three frets down". The patterns for the various scales and arpeggios will show this same simmetry.
First chords: drop2 voicings
We will focus on four note chords, and in particular sevenths chords. Drop2 voicings are usually played on four consecutive strings and are very simple to play. For each seventh chord there are four different drop2 voicing depending on what what chord note we put on top. Let's start with the drop2 shapes for the dominant seventh chord (here sorted by root string)
Dominant Seventh Chords / Drop2 voicings
4,3,1,3,1,7-,1,x,2,5,0,R 4,2,1,7-,0,3,2,R,1,5 4,4,2,5,1,R,6,7-,2,3 4,3,0,R,2,5,4,3,1,7-
These shapes are exactly the same we would have on the first four strings of a guitar with standard tuning. To obtain the same voicing on upper registers, the standard tuning would require you to memorize 8 more shapes (that is, each voicing would correspond to 3 different shapes). As it happens in many other contexts (scales, arpeggios, ...) the fourths tuning doesn't require you to learn more. It simply lets you extend what you already know (or should know) to the whole fretboard.
By lowering the third of the dominant seventh chord we obtain the minor seventh chord (R, 3-, 5, 7-). The shapes for the drop2 voicing can be easily obtained from the above diagrams
Minor Seventh Chords / Drop2 voicings
4,3,0,3-,2,7-,1,x,2,5,0,R 4,3,2,7-,0,3-,4,R,2,5 4,4,2,5,1,R,6,7-,1,3- 4,2,0,R,1,5,2,3-,1,7-
Pretty simple, eh? If we repeat the same trick and raise the seventh of the dominat chord, we obtain a major 7+ chord (R, 3, 5, 7+). Too bad not all voicing obtained modifying the above diagrams will sound good. The last one in particular would have the root on top and the 7+ on the bass. That would create an "artificial" flat ninth, which sounds quite bad. In that situation the 7+ is usually replaced by a 6th (so we have a major chord plus the 6th, with the root on top, which is equivalent to the minor seventh chord based on the 6th).
Major 7+ Chords / Drop2 voicings
4,3,1,3,2,7+,0,x,2,5,0,R 4,3,2,7+,0,3,3,R,2,5 4,5,2,5,2,R,8,7+,2,3 4,3,0,R,2,5,4,3,0,6
The last chord we need to cover the very minimum vocabulary is the halh-diminished. It can be obtained from the minor seventh by lowering the fifth (R, 3-, 5-, 7-), and all the diagrams can be obtained in the same way from those of the minor seventh.
Half Diminished Chords / Drop2 voicings
4,2,0,3-,1,7-,2,5-,0,R 4,3,2,7-,0,3-,4,R,1,5- 4,4,1,5-,2,R,6,7-,1,3- 4,3,1,R,1,5-,4,3-,2,7-
Good! We've covered a lot of territory. These four chords (Dominant, Minor Seventh, Major 7+, Half Diminished) cover all the basic harmonic territory generated by the major scale. No other type of chord can be created there simply by stacking 4 notes on top of each other one third apart. Before moving to more complex chords and voicing let's note a curious fact. If we "raise" the root in the first four diagrams of the Dominant chord we always obtain the same shape:
Diminished Chord / Drop2 shape
This is the drop2 voicing of the diminished chord (R, 3-, 5-, 6. Or R, 3-, 5-, 7--). By lowering any of its notes we obtain back a Dominant chord. The chord is completely symmetric (any note is a minor third away from the adjacent ones) and thus any note can play the role of the root (that's why we have only roots in the above diagram). Let's now see the drop3 voicings!
Drop3 voicings
Drop3 voicings are also very easy to play, and are usually played over five strings (skipping one string between the thumb and the index). The considerations made above still apply identically to the drop3 voicings, so here are the resulting shapes
Dominant Chords / Drop3 voicings
5,3,0,5,4,3,1,7-,5,R 5,3,0,7-,1,x,2,5,0,R,7,3 5,3,0,3,3,R,2,5,6,7- 5,4,0,R,6,7-,2,3,4,x,3,5
Minor Seventh / Drop3 voicings
5,2,0,5,2,3-,1,7-,3,R 5,3,0,7-,1,x,2,5,0,R,6,3- 5,4,0,3-,5,R,3,5,1,x,6,7- 5,4,0,R,6,7-,1,3-,5,x,3,5
Major 7+ / Drop3 voicings
5,3,0,5,4,3,2,7+,4,R 5,3,1,7+,0,x,2,5,0,R,7,3 5,2,0,3,2,R,1,5,3,6 5,5,0,R,8,7+,2,3,5,x,4,5 or 5,4,0,R,5,6,3,3,4,x,3,5 or 5,1,0,R,0,5,0,2,1,3
Half Diminished / Drop3 voicings
5,3,0,5-,4,3-,2,7-,5,R 5,2,0,7-,2,5-,0,R,4,3- 5,4,0,3-,5,R,2,5-,2,x,6,7- 5,4,0,R,6,7-,1,3-,5,x,2,5-
Diminished Chord / Drop3 shape
Altered Dominats
Chords built on the minor scales (harmonic and melodic) are much more varied than then ones obtained from the major scale. It is not my goal to write a book on jazz harmony (thing I wouldn't be able to do anyway) so I will simply present the last family of chords that usually appears in the standard jazz repertoire. Altered dominants. The dominant chord rests on the solid foundation provided by the tritone, the interval of 7 semitones (flat fifth) that occours between its third (e.g. E) and its seventh (e.g Bb). So strong is the sound of the tritone that the Dominant chord can resist a lot of "abuse" and still function in its role. The typical alterations include the the b9, the b13 (both obtained from the fifth mode of the harmonic scale), the #9 (from the seventh mode of the melodic minor), and the b5 or #11 (various modes of the harmonic and melodic minor). Many many voicings and fingering are possible. If we just concentrate our attention to four-note altered dominants (without the fifth) played on the usual sets of strings, we have the following shapes
Altered Dominants / consecutive strings
4,3,0,9-,4,7-,1,3,3,R 4,2,1,9+,1,7-,0,3,2,R 4,2,1,3,0,7-,2,5-,0,R 4,2,1,7-,0,3,2,R,0,5- 4,4,1,3,2,7-,1,x,4,5+,0,R 4,3,1,7-,1,3,3,R,3,5+ 4,4,1,5-,2,R,6,7-,2,3 4,4,1,R,2,5-,6,3,2,7- 4,4,3,5+,0,R,6,7-,2,3 4,3,0,R,3,5+,3,3,1,7-
Altered Dominants / skip one string
5,4,2,7-,2,3,4,x,0,9-,4,R 5,4,0,5-,6,3,2,7-,7,R 5,2,0,5+,2,3,0,7-,3,R 5,2,1,7-,0,3,2,R,2,9- 5,3,0,7-,1,x,1,5-,1,R,7,3 5,3,0,3,3,R,1,5-,7,7- 5,3,0,3,3,R,3,5+,5,7- 5,4,0,R,6,7-,1,9+,5,x,0,3 5,4,0,R,6,7-,2,3,4,x,2,5-
A good way to practice the above chords is the following. Choose a simple tune (e.g. Autumn Leaves, All the things you are), chose a position on the neck (e.g. 7th fret). If you limit yourself to the top five strings you should be able to find the 12 notes once and only once in a fretboard area like the one depicted below
If you keep alternating between drop2 and drop3 voicing and choosing your roots in the above area you should be able to play any tune and chord sequence without changing position. This will usually force you to play shapes you would not have normally chosen (we often tend to stick with what we know instead of trying new roads ...)
More voicings
Another interesting, but less common, voicing is what I call drop24 (drop two four). The fingerings are quite simple for the left hand but require a bit of exercise for the right hand.
Dominants Seventh / drop24
5,3,2,7-,1,3,3,x,2,5,0,R 5,2,1,3,0,7-,3,R,1,5 5,3,2,5,0,R,7,3,1,7- 5,2,0,R,1,5,4,7-,0,3
Minor Seventh / drop24
5,3,2,7-,0,3-,4,x,2,5,0,R 5,1,0,3-,0,7-,1,R,0,5 5,3,2,5,0,R,6,3-,2,7- 5,3,1,R,2,5,6,7-,0,3-
Major / drop24
5,4,3,7+,1,3,4,x,3,5,1,R 5,2,1,3,1,7+,2,R,1,5 5,3,2,5,0,R,7,3,0,6 5,1,0,R,0,5,1,6,0,3
Half Diminished/ drop24
5,3,2,7-,0,3-,4,x,1,5-,1,R 5,2,1,3-,1,7-,3,R,0,5- 5,2,1,5-,0,R,4,3-,1,7- 5,3,1,R,1,5-,7,7-,0,3-
Altered Dominants/ drop24
5,4,3,7-,1,9+,5,x,0,3,4,R 5,3,2,7-,1,3,3,x,1,5-,1,R 5,4,2,7-,2,3,4,x,4,5+,0,R 5,3,2,3,1,7-,5,R,1,5- 5,2,1,3,0,7-,3,R,2,5+ 5,3,0,3,3,R,4,9-,4,7- 5,3,1,5-,1,R,7,3,1,7- 5,4,3,5+,0,R,9,3,2,7-,1,x 5,3,1,R,1,5-,7,7-,1,3 5,2,0,R,2,5+,3,7-,0,3
Chord Scales
Major 6/9: R 2 3 5 6 (mandatory 3)
Major 6/9 | open
4,4,3,R,0,3,4,x,1,2,1,5 4,3,0,R,2,5,4,3,0,6 4,4,0,x,1,2,1,5,5,3,4,R 4,2,0,2,1,6,1,3,2,R 4,5,0,x,3,3,0,5,4,2,4,6,2,x 4,4,2,3,1,6,2,x,3,5,1,R 4,4,2,3,1,6,2,x,3,5,1,x,1,2 4,2,0,3,2,R,1,5,1,2 4,4,0,3,4,R,5,6,1,2 4,3,2,5,0,R,4,6,2,3 4,1,0,5,0,2,0,6,0,3 4,4,0,5,3,2,6,R,0,3 4,4,2,6,1,2,6,R,0,3 4,2,0,6,1,3,2,R,1,5 4,4,0,6,2,x,0,3,4,x,1,2,1,5
Major 6/9 | spread
5,1,0,R,0,5,0,2,1,3 5,3,0,R,4,6,0,2,5,3 5,4,0,R,5,6,3,3,4,x,3,5 5,2,0,2,1,6,1,3,2,x,1,5 5,4,0,2,6,R,0,3,4,x,3,5 5,2,0,3,2,R,1,5,3,6 5,4,0,3,4,x,1,2,1,5,7,6 5,3,0,5,4,3,0,6,6,R 5,4,0,5,5,3,1,6,2,x,5,x,1,2 5,4,0,5,5,3,4,R,5,x,1,2 5,2,0,6,1,3,2,R,3,2 5,4,0,6,2,x,3,5,1,R,9,3
Major 6/9 | split
5,4,3,R,0,3,4,x,5,6,1,2 5,1,0,R,0,5,1,6,0,3 5,3,0,x,1,2,0,5,5,6,2,3 5,4,0,x,1,2,1,5,10,R,0,3 5,4,0,x,1,2,3,6,8,R,0,3 5,3,2,3,0,6,6,R,2,5 5,4,2,3,1,6,2,x,5,x,1,2,1,5 5,3,1,3,3,R,3,x,1,2,0,5 5,2,0,3,2,R,3,2,1,6 5,3,2,5,0,R,7,3,0,6 5,3,2,5,0,x,1,2,5,3,0,6 5,2,0,5,1,2,3,3,2,R 5,3,2,6,0,2,5,3,3,R 5,3,1,6,2,3,3,x,2,5,0,R 5,2,0,6,1,3,2,x,1,5,1,2
7: R 2 3 5 6 7- (mandatory 3, 7-)
7 | open
4,3,0,R,2,5,4,3,1,7- 4,3,0,R,4,6,2,3,1,7- 4,3,0,x,1,2,0,5,4,3,1,7- 4,2,1,2,1,6,1,3,0,7- 4,2,0,2,2,7-,0,3,2,R 4,3,1,3,1,7-,1,x,2,5,0,R 4,3,1,3,1,7-,1,x,2,5,0,x,1,2 4,4,2,5,1,R,6,7-,2,3 4,2,0,5,1,2,2,7-,0,3 4,5,4,6,0,R,7,7-,3,3 4,3,2,6,0,2,3,7-,1,3 4,3,1,6,2,3,1,7-,1,x,2,5 4,2,1,7-,0,3,2,R,1,5 4,4,1,7-,1,x,0,3,4,x,1,2,1,5
7 | spread
5,4,0,R,6,7-,0,2,6,x,0,3 5,4,0,R,6,7-,2,3,4,x,3,5 5,2,0,2,2,7-,0,3,2,x,1,5 5,3,0,3,3,R,2,5,6,7- 5,4,0,3,4,R,5,6,6,7- 5,4,0,3,4,x,1,2,3,6,6,7- 5,4,1,5,5,3,1,6,6,7-,1,x 5,3,0,5,4,3,1,7-,5,R 5,4,0,5,5,3,2,7-,1,x,5,x,1,2 5,2,1,6,1,3,0,7-,3,R 5,3,1,6,2,3,1,7-,1,x,3,x,1,2 5,2,1,7-,0,3,2,R,3,2 5,3,0,7-,1,x,2,5,0,R,7,3 5,3,0,7-,1,x,2,5,0,x,1,2,5,3 5,5,0,7-,1,x,4,5,2,x,3,3,5,2
7 | split
5,2,0,R,1,5,4,7-,0,3 5,3,0,R,4,6,4,7-,1,3 5,3,0,x,1,2,0,5,6,7-,1,3 5,3,0,x,1,2,2,6,4,7-,1,3 5,4,0,x,1,2,4,7-,7,R,0,3 5,3,0,3,3,R,5,2,3,7- 5,4,3,3,1,6,6,7-,1,x,3,5 5,5,2,3,2,6,2,x,7,x,1,2,5,7- 5,2,1,3,0,7-,3,R,1,5 5,3,1,3,1,7-,1,x,3,x,1,2,0,5 5,3,2,5,0,R,7,3,1,7- 5,2,1,5,1,2,3,3,0,7- 5,4,3,6,1,2,7,3,2,7-,1,x 5,4,3,7-,0,2,6,x,0,3,4,R 5,3,2,7-,1,3,3,x,2,5,0,R 5,2,1,7-,0,3,2,x,1,5,1,2
7+: R 2 3 5 6 7+ (mandatory 3, 7+)
7+ | open
4,5,0,R,8,7+,2,3,2,6,2,x 4,3,0,x,1,2,0,5,4,3,2,7+ 4,1,0,2,0,6,0,3,0,7+ 4,3,0,2,4,7+,0,3,3,R 4,5,0,x,3,3,0,5,4,2,6,7+,0,x 4,5,0,x,3,3,2,6,2,2,6,7+,0,x 4,4,2,3,1,6,2,x,3,5,0,7+,0,x 4,3,1,3,2,7+,0,x,2,5,0,R 4,2,0,3,1,7+,0,x,1,5,1,2 4,4,0,3,3,7+,0,x,5,6,1,2 4,5,2,5,2,R,8,7+,2,3 4,3,0,5,2,2,4,7+,0,3 4,5,4,6,0,R,8,7+,2,3 4,3,2,6,0,2,4,7+,0,3 4,2,0,6,1,3,1,7+,0,x,1,5 4,5,4,7+,0,2,4,6,2,x,1,3 4,5,4,7+,2,3,2,6,2,x,4,5 4,3,2,7+,0,3,3,R,2,5 4,4,2,7+,0,x,0,3,4,x,1,2,1,5 4,4,2,7+,0,x,0,3,4,R,5,6 4,4,2,7+,0,x,0,3,4,x,1,2,3,6 4,4,0,7+,0,x,3,5,5,3,1,6
7+ | spread
5,5,0,R,8,7+,0,2,7,x,1,3 5,5,0,R,8,7+,2,3,5,x,4,5 5,3,0,2,4,7+,0,3,3,x,2,5 5,4,0,2,5,7+,0,x,0,3,4,x,5,6 5,2,0,3,1,7+,0,x,1,5,3,6 5,3,0,5,4,3,2,7+,4,R 5,4,0,5,5,3,3,7+,0,x,5,x,1,2 5,2,1,6,1,3,1,7+,2,R 5,2,0,6,1,3,1,7+,0,x,3,2 5,5,4,7+,2,3,2,6,2,x,7,x,1,2 5,3,2,7+,0,3,3,R,5,2 5,2,0,7+,0,x,1,5,1,2,3,3 5,4,0,7+,0,x,5,6,1,2,7,3
Scales and Arpeggios
Learning scales and arpeggios on the P4 is a lot simpler than on the normal tuning. If you already know your scales/modes/arpeggios on the normal tuning, then you can already play them on the P4. You simply have to "unlearn" that little bump caused by the majord third between the G and B strings, and simply use the shapes that you have learned on the first four strings. At first it will feel a bit strange, but you'll get over it very quickly, and it will feel completely right. No exceptions anymore.
Major scale
Melodic Minor scale
Harmonic Minor scale
Diminished scale
Whole Tone scale